Underwater signaling and apparatus therefor



Sept. 25, 1962 1.. M. DE KANSKI ETAL 3,056,104

UNDERWATER SIGNALING AND APPARATUS THEREFOR 8 Sheets-Sheet 1 Filed May 1, 1959 FIG. 3

INVENTORS LEON M. DaKANSKI AT TOR/VE Y S Sept. 25, 1962 L. M. DE KANSKI ETAL 3,056,104

UNDERWATER SIGNALING AND APPARATUS THEREFOR FIG. 4

N 8; A N

m m S //v NTORS "3 (Y) D SKI yaw /79 J G 1. M m T E DORE E. DINSMOOR NORMAN w. NARD N PIO F. MAR UZZI BY M ATTORNEYS Sept. 25, 1962 L. M. DE KANSKI ETAL UNDERWATER SIGNALING AND APPARATUS THEREFOR Filed May 1, 1959 HETERODYNE FILTER STAGGER TUNED HETERODYNE 500 CPS -IOO KC SELF- SEEKING, NAR- ROW BAND FILTER SIGNAL DISPLAY 8 Sheets-Sheet 3 INVENTORS LEON M. DeKANSKl THEODORE E. DINSMOOR NORMAN w. GUINARD PIO F. MARTINUZZI ATTORNEYS Sept. 25, 1962 L. M. DE KANSKI ETAL 3,056,104

UNDERWATER SIGNALING AND APPARATUS THEREFOR Filed May 1, 1959 8 Sheets-Sheet 5 FIG. ll

INVENTORS LEON M. DeKANSKI THEODORE E. DINSMOOR NORMAN w. GUINARD PIO F. MARTINUZZI BY v We! 7 z ATTORNEYS Sept. 25, 1962 M. DE 'KANSKI ETAL 3,056,104

UNDERWATER SIGNALING AND APPARATUS THEREFOR Filed May 1, 1959 FIG. I2

8 Sheets-Sheet 6 FIG. I3

LEON M. DOKANSKI 7 94 INVENTORS THEODORE E. DINSMOOR NORMAN W. GUINARD BY PIO. F. M'ARTINUZZI ex ATTORNEYS L. M. DE KANSKI ETAL 3,056,104

8 Sheets-Sheet 7 Sept. 25, 1962 UNDERWATER SIGNALING AND APPARATUS THEREFOR Fi led May 1, 1959 I ATTORNEYS Sept. 25, 1962 DE KANSKI ETAL UNDERWATER SIGNALING AND APPARATUS THEREFOR Filed May 1, 1959 8 Sheets-Sheet 8 FIG. I5 4 g a Q I I I 7 7 I7 775 T /55 T T755 "222225.22- J 0F A0 L Y PICKOFF FREQUENCY FREQUENC DEVICE SIGNAL SIGNAL 763 769 770 ALGEBRAIC REFERENCE ADDER 7 SD SE R VOLTAGE (FREQUENCY) SOURCE SERVO SERVO AMPLIFIER MOTOR AMPLIFIER MOTOR FUEL HIGH PRESSURE AIR INVENTORS PIO F.

MARTINUZZI A T TORNEYS United States Patent Ofilice Fatented Sept. 25, 1962 3,056,104 UNDERWATER SIGNALING AND APPARATUS THEREFGR Leon M. De Kanski, Cos Cob, Conn, Theodore E. Dinsmoor, Silver Spring, Md, Norman W. Guinard, Arlington, Va, and Pie F. Martinuazi, Hobolten, N31, assignors to American Machine & Foundry Company, a corporation of New Jersey Filed May 1, I959, Ser. No. 810,500

42 Claims. (Cl. 340-5) This invention relates to the art of underwater signaling by the generation, propagation and reception of acoustic energy.

For the purposes of the present application, the term signaling is used generically to define all procedures in which purposefully created energy is received at a distance to accomplish a desired result. Thus, the invention is applicable, for example, to the detection of underwater bodies by causing acoustic energy to be transmitted to and reflected by the underwater body, the reflected energy being received, at a point remote from the underwater body, and a signal indicative of the presence of the body derived from the received energy. The invention is also applicable to underwater communication broadly, and to the automatic actuation of remotely located underwater devices.

Prior-art underwater signaling systems, such as the conventional sonar systems, are capable of operating effectively over ranges which are relatively short. Thus, with known sonar, good operation is attained at ranges of a few miles. The present invention provides an underwater signalling system capable of effective operation not only over the relatively short ranges heretofore attainable with prior-art equipment but also over very long ranges, up to 1500 or more miles. Successful operation of an underwater signaling system over such extremely long ranges is made possible in accordance with the invention by the provision of means for generating the signaling energy at a power level of a magnitude heretofore impossible to attain.

While the invention is useful for many purposes, its main advantages can be well understood in connection with its use in a sea surveillance system. for accomplishing, at long range, the purposes heretofore accomplished at short range by conventional sonar systems. In conventional sonar systems, a transducer, such as a piezoelectric or magnetostrictive type, is employed as an acous tic generator to effect propagation in the water of sonic or ultrasonic energy, the propagated wave energy travelling to the underwater body or target, being reflected thereby and received at the point of propagation. The frequency of the acoustic wave so employed generally ranges from 5 kilocycles (kc.) upwardly.

As the energy radiates from its point of generation, attenuation occurs for various reasons, particularly including spreading loss and absorption loss. The absorp tion loss depends upon the operating frequency and, we have found, increases with increasing frequency. Conversely, the absorption losses can become practically insignificant when the operating frequency is decreased.

If a conventional sonar system, employing a piezoelectric or magnetostrictive transducer as an energy generator, were constructed to operate over a range of even 500 miles at an operating frequency of 500 cycles per second (c.p.s.), calculations indicate that the energy generator would have to have an output of about 1 megawatt, and that the weight of the generator would be on the order of 1 million pounds. Were it desired to increase the range of such a system to 1,500 miles, the power output of the generator would have to be increased approximately 1,000 times.

In considering the possibility of providing an underwater signaling system practical for long range operation, it is thus immediately apparent that the energy generators heretofore employed are entirely unsuitable, and that other energy generators must be considered. In view of the very high power requirements, it would at first appear that a simple explosion device would sufiice. It can be demonstrated, however, that a simple explosion device capable of producing the high level of acoustic energy necessary for long range echo ranging would have to exhibit power on the order of magnitude of that provided by an atomic explosion.

In general, the present invention overcomes the aforementioned problems, making long range underwater signaling practical. Underwater signaling systems in accordance with the invention include as the acoustic energy generator a device including a member mounted for rectilinear movement and having an energy generating surface disposed for direct contact with the Water when the device is immersed, and a combustion engine connected to reciprocate such member at a relatively low frequency, such as from a few c.p.s. to c.p.s., for example, the arrangement being such that the engine directly and positively drives the energy generating member, through at least one-half of its cycle of reciprocatory movement, with relatively great power, the power output of the engine being on the order of from a few kilowatts to 1.5 megawatts or higher. In certain embodiments, the energy generating member is positively driven by the combustion engine in both directions; in other embodiments, such member is positively driven in one direction by the engine and positively returned by the pressure of the water in which the device is immersed. In all cases, the energy generating surface is positively driven, with relatively great power, in true rectilinear fashion at low frequency, with substantially constant predetermined amplitude of movement, to generate acoustic wave energy transmitted primarily by a compressional wave of corresponding low frequency and relatively long wave length.

When the invention is employed for detection of underwater bodies at long range, the acoustic energy produced in the manner just described is reflected from the body to be detected, and the reflected energy is received, as by conventional transducer means, along with the usual broad spectrum of noise and other signals always present in large bodies of water. The desired reflected low frequency signal is then isolated from the broad background spectrum in a novel fashion later described in detail. Since the object being detected may be more than 1,000 miles from the propagation point, it is obvious that attenuation of the compressional wave energy will be such that, even in view of the large amount of energy generated, the reflected energy is relatively small, at the reception point, relative to the background energy spectrum. t is accord-. ingly necessary to employ special techniques for isolation of the desired signal from the electrical output of the receiving transducer means.

When the invention is employed for direct underwater communication, as between a shore station and a submarine, the low frequency, high power acoustic energy is not reflected, but rather travels directly from the point of its propagation to the receiver. Under such conditions, the energy is less attenuated, a lower power energy generator can thus be used, and the problems involved in recovery of the desired signal are less severe than in systems for detecting underwater bodies.

A general object of the present invention is to provide an underwater signaling system capable of practical operation over long ranges.

Another object is to devise an improved system for detection and/or location of underwater bodies by means 3 of acoustic energy propagated in the water and received after being reflected from the body to be detected or located, such system being practical for use over ranges never attainable with sonar systems hereinbefore available.

An additional object is to provide a long range underwater signaling system employing acoustic energy propagated in the water at unusually low frequency and unusually high energy levels.

A further object is to provide a novel and improved device for generating acoustic wave energy in water.

Yet another object is to devise a novel underwater device capable of generating compressional wave energy of substantially sinusoidal form at frequencies on the order of from a few c.p.s. to 100 c.p.s., for example, and at power levels in the range of from a few kilowatts to 1.5 megawatts or greater.

A still further object is to devise an underwater acoustic energy generator suitable for practical operation at relatively great depths.

An additional object is to devise a system for detection of underwater bodies by means of reflected acoustic energy of low frequency, such system including novel and improved means for propagating the desired energy and unusually effective means for deriving from the reflected energy a signal representative of the presence of the underwater body being detected.

In order that the manner in which these and other objects are attained in accordance with the invention can be understood in detail, reference is had to the accompanying drawings, which form a part of this specification, and wherein:

FIGURE 1 is an elevational view of a complete underwater energy generating unit constructed in accordance with the invention;

FIGURE 2 is a top plan View of the unit of FIGURE 1;

FIGURE 3 is a sectional view taken on line 33, FIG- FIGURE 4 is a longitudinal sectional view, with some parts shown in elevation, of a free-piston engine mass oscillator apparatus forming part of the unit shown in FIGURE 1;

FIGURE 5 is a perspective view of the piston assembly of the apparatus illustrated in FIGURE 4;

FIGURE 6 is a transverse sectional view taken on line 6-6 of FIGURE 4;

FIGURE 7 is a transverse sectional view taken on line 77, FIGURE 4;

FIGURE 8 is a schematic diagram of a complete signaling system in accordance with the invention and operative for long range detection of underwater bodies;

FIGURE 9 is a schematic diagram of a second signaling system in accordance with the invention and operative for direct underwater communication or the actuation of remotely located underwater devices;

FIGURE 10 is a longitudinal sectional view, with some parts shown in elevation, of another embodiment of free-piston engine apparatus useful in the unit of FIG- URE 1;

FIGURE 11 is a partial longitudinal sectional view of a modified form of the free-piston engine device shown in FIGURE 10;

FIGURE 12 is a longitudinal sectional semi-diagrammatic view, with some parts shown in elevation, of a further embodiment of a free-piston engine device useful in accordance with the invention;

FIGURE 13 is a view, partly in elevation and partly in section, of an acoustic energy generating unit embodying the free-piston engine device of FIGURE 12;

FIGURE 14 is a schematic diagram of one form of starting and operating control system useful with the combustion engine devices of the invention, and

FIGURE 15 is a schematic diagram of another form of operating control system useful with the combustion engine devices of the invention.

4 Referring now to the drawings, certain illustrative embodiments of the invention will be described in detail.

Submerged Acoustic Energy Generator Unit From FIGURES 1-3, it will be seen that the submerged acoustic wave energy generating unit here illustrated comprises a cylindrical power device housing 1. This housing may be carried by and extend transversely through a streamlined body 2 provided with stabilizing tail fins 3 and a towing and supporting harness 4. Harness 4 is secured to longitudinally spaced points on housing 1 so that the longitudinal axis of the housing can be oriented in a desired position. Swiveled to the harness 4 is a connector 5 to which is fixed the end of a hollow towing and supporting cable 6, the cable 6 enclosing an electrical supply cable 7a and a fuel supply line 7, which extends through a suitable sealed joint (not shown) from connector 5 to the interior of body 2. Tied to cable 6, as indicated at 8, is a flexible fluid-tight exhaust conduit 9 within which extends a smaller diameter flexible high pressure air hose 10. The conduit 9 enters body 2 via a sealed joint indicated at 11, FIGURE 2.

As seen in FIGURE 3, the cylindrical housing 1 is closed at each end by the combination of a circular energy propogating plate or acoustic piston 12 and an annular flexible metal diaphragm 13, the circular inner and outer edge portions of the diaphragms being clamped in fluidtight relation, in any suitable fashion, respectively to the housing 1 and plates 12. Plates or acoustic pistons 12 are relatively thick and, for practical purposes, rigid. Each plate 12 is rigidly secured to the cylinder body 14 of a free-piston engine device 15 supported in housing 1 in any suitable manner, as for example by pivoted links 16, for reciprocatory movement axially within and relative to the housing.

Each free-piston engine device 15 has its inner end spaced from the center of housing 1 and the housing mounts a transversely extending rigid member 17 provided to support a synchronizing linkage for the two freepiston engine devices. The synchronizing linkage comprises a lever 18 attached at its center to member 17 by means of a shaft 17 fixed to lever 18 and journaled in member 17. The free ends of lever 18 are pivotally connected to one end of links 19. The other ends of links 19 are each pivoted to a different one of the free-piston engine devices 15.

In addition to the synchronizing linkage just described, the two free-piston engine devices 15 are interconnected by a centering spring, indicated diagrammatically at 18 operative, in combination with other elasticities presented in the structure, such as the elasticity of diaphragms 13, to fix the center points about which the two cylinder bodies 14 reciprocate. Spring 18 can be of any conventional construction offering elasticity in both directions axially of the free-piston engine devices and can be interposed between the two cylinder bodies in any suitable fashion.

As seen in FIGURES 4-7, each free-piston engine device 15 comprises the cylinder body 14 and a piston assembly 20. Body 14 comprises sections 14*, 14 secured together, as by bolts (not shown). Body sections 14 and 14 define a pair of axially extending, parallel, spaced end cylinders 21. Body sections 14 and 14 also define a chamber 22 disposed at the outer ends of cylinders 21 and with which both cylinders communicate. Body section 14 also defines a central cylinder 23, substantially larger in diameter than cylinders 21. The longitudinal axes of cylinders 21 are coplanar, and are equally spaced from the longitudinal axis of cylinder 23.

The piston assembly 20 comprises a central piston 26, dimensioned to work in cylinder 23, and pairs of opposed end pistons 27 projecting from opposite faces of piston 26 and dimensioned to work in cylinders 21. Pistons 26 and 27 constitute a single operating unit. As will be clear from FIGURE 5, the longitudinal axes of pistons 27 are coplanar and equally spaced from the longitudinal axis of piston 26.

Operatively disposed to deliver fuel to each chamber 22 is a pair of fuel injectors 29, of conventional construction, each aligned with a different one of cylinders 21. Each cylinder 21 in body sections 14 and 14 is provided with a lateral exhaust port 30 and a lateral scavenging air inlet port 31 connected, via duct 32 to a port 36 in the wall of cylinder 23. It will be evident from FIGURE 4 that the cylinder arrangement of engine device 15 is symmetrical about port 36.

Air under relatively high pressure (e.g., up to 1,000 pounds per square inch) is supplied to cylinder 23, via air hose 10, and air inlet manifold FIGURES 1 and 4, and supply ducts 37, FIGURE 4, in body sections 14 and 14 the supply of air being controlled by suitable valves, as hereinafter described with reference to FIGURE 14. The device is provided with two ducts 37, and the corresponding valves, each duct 37 being disposed to deliver air to cylinder 23 through a different end wall of the cylinder and alternately to opposite sides of piston 26.

Chambers 22 constitute diesel combustion chambers, the injectors 29 being effective to inject diesel fuel delivered thereto by fuel line 7 The injectors are cycled, by suitable mechanism 33, such as Bosch jerk pump units, to deliver fuel charges alternately, first to one diesel combustion chamber 22, and then to the other, as described hereinafter with reference to FIGURE 14. Simultaneously with combustion of the fuel mixture in one chamber 22, its respective air inlet valve is opened, as described more in detail hereinafter, to allow high pressure compressed air to enter cylinder 23 behind piston 26. The combined expansion of this air and combustion of the gases provide the total power of the engine cycle. The air pressure provided is sufiicient to effectively scavenge the cylinders and also exhaust against the back pressure of water at the exhaust outlet of the engine, which may be at a depth of several hundred feet.

When port 36 is opened by the movement of piston 26, air in cylinder 23 on the pressure side of piston 26, flows through duct 32, thence into cylinders 21 and through the corresponding chamber 22 in the body portion 14 or 14 being scavenged, and thence out of the corresponding exhaust port 30 to complete scavenging.

The exhaust gases are led, via suitable ducting and exhaust manifold 9 to exhaust conduit 9 and, therefore, flow upwardly in the space surrounding air hose 10. This arrangement represents an exhaust-to-feed air heat exchanger, whereby the efliciency of operation is enhanced.

Expansion of the burning fuel charge, aided by expansion of air in cylinder 23, causes relative rectilinear movement between the cylinder body 14 and the piston assembly 20 until piston 26 reaches a position at the opposite end of cylinder 23, the cycle of operation then being repeated in the opposite direction.

Cylinder body 14 and plate 12, together with the inertial load of water, constitute a substantial mass M While piston assembly 20 constitutes a substantial mass M During continual operation in the manner just explained, mass M can be said to have a stroke A and assembly 20 a stroke A the relationship therebetween being expressed as an approximation by the formula:

z ii It is thus obvious that the device can be so designed as to provide a powerful reciprocatory output of predetermined amplitude.

As will be clear from FIGURE 4, energy propagating plate or acoustic piston 12 is secured rigidly to body 14 of the corresponding free-piston engine device 15, as by a plurality of radially disposed plates 39. With reference to FIGURE 3, the two free-piston engine devices 15 are 6 synchronized in operation by the synchronizing linkage comprising elements 1 8 and 19 in combination with proper timing of the fuel injectors 29 and the air inlet valves. It is clear, therefore, that the plates 12 will be reciprocated axially relative to housing 1. It is to be further noted that the frequency of operation of the freepiston engine devices 15 can be predetermined as desired, being dependent upon the cycling of the diesel fuel injectors, the operation of the air inlet valves and the design parameters of the device. The operating frequency can be maintained substantially constant in operation by a suitable control system, such as that described hereinbelow.

In use, the acoustic generator described with reference to FIGURES l-7 is submerged, preferably below the thermocline, at great depths, and is operated in such fashion that the acoustic pistons .12 are reciprocated colinearly and axially relative to housing 1 with a suitable frequency and amplitude determined in accordance with acoustical requirements, such as acoustic pressure and depth of operation. The interior of housing 1, if desired, may be suitably pressurized with air or other suitable fluid to balance the hydrostatic pressure applied exteriorly at the particular operating depth. The exhaust conduit 9 can be extended to the surface or terminated at some suitable intermediate depth, the exhaust gases being discharged into the water, in the latter case, with satisfactory operation being assured because of the relatively high discharge pressure accomplished because of the combined compressed air and diesel cycle.

Plates 12 can be made large, as on the order of 60" in diameter, and for some purposes, the free-piston engine devices can be designed with a power output on the order of 1350 HP, giving a power rating of at least one megawatt for the energy generating unit. For such specifications, each free-piston engine device 15 can be as small as 52 in length and 16" in maximum transverse dimension. The invention also contemplates the use of freepiston engines having considerably lower power output.

Since plates 12 are positively driven by the free-piston engine devices 15, and since plates 12 are essentially rigid, it is obvious that the unit is effective to produce acoustic waves of the desired frequency and amplitude with a relatively small overtone content.

System for Long Range Detection of Underwater Bodies FIGURE 8 illustrates diagrammatically application of the invention to the long range detection of underwater bodies. Here, the unit described with reference to FIG- URES 1-7 is submerged at considerable depth, said 500, and is operated with plates 12 reciprocating through an amplitude of, for example, 3 at 30-100 cycles per second. So operated, the unit A generates a compressional Wave at such frequency and at such a high level that the propagated energy is capable of traveling great distances, say 1,000 miles, to contact an underwater object such as the submarine indicated at B and be reflected therefrom for reception by the usual directional receiving transducer array C. Assuming the range to be 1,000 miles, and the receiving transducer array C to be located near the energy generator A, the energy generator can be operated for successive 2 second periods spaced by 2.5 second listening periods.

Receiving transducer array C provides an electrical output comprising (1) a signal representative of the low frequency, substantially sinusoidal longitudinal Wave energy reflected from the target to the transducer array and (2) interference or background signals, both coherent and non-coherent, resulting from conditions inherently present in the sea and other large bodies of water, the background or interference signal power level being as much as 1 0 times as strong, in a one-cycle band, as the signal power level produced by energy reflected from the target. Such electrical output is heterodyned, or multiplied in any suitable fashion, to increase the frequency of the desired signal, and is then passed through a stagger tuned filter D providing a narrow flat band pass at relatively low frequencies. The signal passed by the filter D is then again increased to a relatively high frequency, such as 100 kc., and supplied to a device E characterized by the ability to act as a movable or self-seeking filter of constant narrow band width. Device E can be an AFPC loop of the type described in Naval Research Laboratory Report No. 4630, entitled An Active Filter, by G. K. Jensen and J. E. McGeogh, published November 10, 1955, by the Department of the Navy, Oflice of Naval Research, constructed to pass 100 kilocycles 3:.05 cycle per second. excluding substantially all else, and following the desired signal as the same changes frequency.

The stagger tuned filter E thus serves the preliminary purpose of deriving from the transducer output, at relatively lower frequency, a complex signal of relatively narrow band width including the desired signal and suitable, when increased in frequency, to the operational characteristics of the narrow band width self-seeking filter E.

The essentially pure signal provided as the output from filter E is then supplied to any conventional signal display or recording device F capable of displaying the signal, or its detected envelope, in a meaningful fashion.

The system just described diifers from prior-art sonar and like systems for detection of underwater bodies in several respects, the primary difference being that the present system is, to our knowledge, the first ever devised which can be operated over ranges in excess of 500 miles. This unique capability of operation over long ranges is made possible by the fact that the propagated acoustic energy is of unusually low frequency and is generated in substantially sinusoidal form at power levels, not heretofore attainable by practical means, sufiiciently high to provide detectable reflected energy even in view of the great attenuation occurring when the reflecting target is located at such great distances from the energy generator.

The system illustrated in FIGURE 8 is especially useful in carrying out long range sea surveillance. Energy generator A, constructed in accordance with FIGURES 1-7, is capable of use at great depths for long periods of time. With the system used continuously, day after day, it is possible to detect and follow all objects of significant size within a range of as much as 1500 miles.

Direct Underwater Communication System For those applications necessitating only the direct reception of energy under water, the system of the invention can be represented as seen in FIGURE 9. Here, the energy generator A is submerged and oriented to radiate acoustic energy toward the point of reception, at which receiver G is located.

Here, the energy generator A can be constructed in accordance with FIGURES 1-7, but with a lower power output. The receiver G can take the form described with reference to FIGURE 8, so providing a representation of the transmitted signal in pure form, or can be a more rudimentary device.

Alternative Free-Piston Engine Device of FIGURE 10 While, in the embodiment shown in FIGURES l7, the energy generating members 12 are each fixed to a moving portion of a different one of the free-piston engine devices 15, the latter are so constructed as to drive said members positively in both directions. Another embodiment using a different arrangement for engine energy-towater transmission is shown in FIGURE 10.

Here, the free-piston engine device l5 comprises a generally cylindrical body member 50 defining a central cylindrical bore or combustion chamber 51, of relatively smaller diameter, and end cylindrical bores 52, of larger diameter. Body member 15 is mounted within cylindrical housing 1 by a pair of rigid frusto-conical members 53 each having a centrally disposed, flat circular wall 8 54 which closes the outer end of the corresponding bore 52 of body member 50. The periphery of each member 53 is secured to the inner surface of a different end portion of housing 1*.

Two identical piston assemblies 55 are employed, each comprising a larger short piston 56, a smaller long piston 57, and a plunger 58. Pistons 57 are disposed in the opposite end portions of central cylindrical bore $1, the adjacent ends of pistons 57 combining with the wall of bore 51 to define a combustion chamber. Dimensioned to work in cylindrical end bores 52, pistons 56 are short relative to the length of bore portions 52 and are allowed a stroke indicated at 56 Each wall 54, forming an end cap for body 50, is provided with a bore to accommodate the corresponding plunger 58 and fluid tight seals are provided between the plungers and walls 54 in any suitable manner. The outer end of each member 53 is closed by the combination of a substantially rigid circular plate 12 and an annular flexible diaphragm 13 The chamber defined by each member 53 and its associated wall 54, plate 12 and diaphragm 13 is filled with a substantially incompressible liquid L.

A fuel injector 59 is mounted in a suitable bore in body 50 to inject diesel fuel into the space between the adjacent ends of pistons 57. Adjacent each end of central bore 51, body St is provided with an air inlet duct 60 communicating via port 61 and duct 62 with the space between piston 56 and the adjacent end wall of cylindrical bore 52. Port 61 is controlled by a suitable valve 63. Each cylindrical bore 52 is provided with a lateral port 64 communicating via duct 65 with a lateral port 66 in central bore 51. Bore 51 is also provided with outlet ports, indicated at 67, leading to suitable exhaust ducting in the general fashion described with reference to FIGURES 1-7.

In operation, assuming the necessary quantity of air has been introduced into the combustion chamber 51, a fuel charge is injected, by an injector 59 of suitable conventional design, into the same chamber. Ignition of the charge drives the piston assemblies 55 outwardly. Simultaneously, compressed air under relatively high pressure, supplied via hose 10, FIGURE 1, is admitted behind pistons 56 by valves 63, and the power of the expansion of the air is added to the diesel power cycle. As pistons 56 travel outwardly, ports 64 are uncovered, allowing the air to escape from bores 52 and scavenge bore 51, exhausting via ports 67 and being ultimately delivered to the exhaust conduit (not shown) which can be similar to conduit 9 shown in FIGURE 1. Valves 63 are again closed at a suitable point in the cycle, thereby preparing the engine for the next cycle.

Outward movement of plungers 58 causes a displacement of the liquid L in chambers 53, and hence results in linear outward movement of energy generating plates 12 The stroke of said plates is determined primarily by the ratio of the displacement of plunger 58 to the area of plate 12*, and thus can be designed to meet the required acoustic radiation parameters. Upon reverse movement of piston assemblies 55, plungers 58 are retracted, allowing the hydrostatic pressure existing at the outer faces of plates 12 to force the plates back to their initial positions. Hence, though power is applied to plates 12 by the free-piston engine device only in one direction, the combination of such power application and the opposing hydrostatic pressure serves to positively reciprocate the energy generating plates through a predetermined amplitude.

The Embodiment of FIGURE 11 FIGURE 11 discloses a further embodiment of freepiston engine which can be used in practicing the invention. The construction and operation are essentially the same as those of the engine disclosed in FIGURE 10. The prime difference resides in the direct coupling or attachment of plungers 58 to plates 12*.

Alternative Free-Piston Engine Device of FIGURE 12 FIGURE 12 illustrates yet another form of freepiston engine device useful in accordance with the invention for generating acoustic energy unde water. Here, the device comprises a hollow body structure 75 defining a centrally disposed cylinder 76-, of larger diameter, and end cylinders 77, of smaller diameter, aligned co-axially with the central cylinder, the cylinders being separated by walls 70. The device again employs a unitary piston assembly, indicated generally at '79, comprising a piston rod 80, a centrally disposed larger piston 01 and end pistons 82. Piston 81 is dimensioned for operation in central cylinder 76 and pistons 02 for opera tion in end cylinders '77, as shown.

Diesel fuel injectors $3 of suitable conventional type are mounted to inject fuel charges into the portions of end cylinders 77 disposed outwardly of pistons 82. The two fuel injectors 82 are actuated to operate sequentially, thus providing a high energy double action cycle.

Each end cylinder 77 is provided, at its outer end, with an inlet port 84 controlled by a suitable valve 85 and communicating with a duct 06 to which compressed air is supplied at pressures in accordance with known diesel engine practice. Each cylinder 77 is also provided with a lateral port 87 controlled by valve 88 and communicating with duct 89 leading to a lateral port 90 in central cylinder 76. The two ports 90 are disposed each adjacent a different end of cylinder 76. Similarly disposed are two exhaust ports 91, each controlled by a valve 92 and communicating with an exhaust duct 93.

Thus, FIGURE 12 represents a double action freepiston diesel engine provided with a special device to aid evacuation of the exhaust gases against high back pressure resulting from operation of the device when submerged at great depths. This device is embodied in the central part of the engine and comprises the cylinder 76, piston 81 and a series of valves and ducts 88, 09, 92 and 93. Its action can be explained by stating that during the power stroke in each diesel cylinder 77, there is created in the adjacent part of the cylinder 76 a certain degree of vacuum which evacuates the combustion gases from the said diesel cylinder. When the stroke reverses, valve 88 closes and valve 92 opens and the piston 81 expels the combustion gases against back pressure through opening 93.

During the subsequent /2 stroke occurring in reversed direction, the valve 87 closes, valve 91 opens and the combustion gases are expelled forcibly by the piston 81 through valve 91 and duct 93 against pressure prevailing outside of valve 91.

Assuming the ports to be in the relative positions shown in FIGURE 10, fuel is injected into the left hand one of cylinders 77 and ignition of the fuel causes relative linear movement between piston assembly 79 and cylinder body 75 in a sense such that the piston assembly may be considered as moving to the right, as viewed in the drawings. Toward the end of this stroke, the left hand one of valves 85 opens to admit compressed air to this cylinder. By this time port 87 is uncovered. The expanding air then elfects scavenging of the combustion gases, which are delivered into the left portion of cylinder 76, as viewed in FIGURE 12. The cycle is then repeated, with fuel injection now at the opposite end of the device.

It will thus be understood that continual operation of the free-piston engine device causes reciprocatory axial movement of cylinder body 75 and that the amplitude of such movement can be predetermined in the manner hereinbefore explained.

free-piston engine device of the type described with reference to FIGURE 12 can be employed in an underwater signaling system in accordance with the invention. Here, a pair of reciprocating engines of the type shown in FIG- URE 12 are disposed co-axially within a cylindrical housing 94, the engines being mounted for free axial reciprocation relative to the housing by any suitable means, such as bearing rollers indicated at 95. Rigidly secured to the outwardly disposed end of each engine is a rigid acoustic piston 96. Each piston 96 is connected to the adjacent end of housing 94 in fluid-tight fashion, as by a bellows 97.

The unit is provided with an upper spherical float 98 having suflicient buoyancy to maintain the unit in upright position, with the axes of the free-piston devices extending horizontally. Float is rigidly connected to housing 94, as by a tubular column 99. At its top, the float is provided with a towing eye 100, for attachment to a suitable chain 101. The supply cables and conduits necessary to carry out submerged operation of the freepiston engine devices are led along the towing chain 101 and connected by suitable couplings to the float 98, the cables and conduits then extending downwardly through tubular column 99, and an appropriate opening in the wall of housing 94, for connection to the free-piston devices. There can thus be provided an exhaust conduit 102, a high pressure air hose 103 and a fuel line 104.

In operation, with the free-piston engine devices functioning in the manner hereinbefore described with reference to FIGURE 12, the bodies 75 are reciprocated axially relative to housing 94 and energy generating plates 96 are accordingly reciprocated, being positively driven in both directions.

It is important to note in this embodiment that no laterally exposed part of the apparatus reciprooates except the plates 96. Movement of the bellows 97 is substantially ineffective to modify the acoustic wave energy generated by movement of the plates 96, since the bellows are located behind the plates, rather than peripherally thereof. This embodiment of the invention is accordingly particularly well adapted for the generation of substantially pure sinusoidal acoustic wave energy.

To enhance the last-mentioned feature, the two freepiston engine body structures 75 are each connected, as by shafts 105, to an energy storing device indicated generally at 106 and disposed between the two free-piston engine devices. The energy storing device can, for example, be a hydraulic spring comprising two opposed pistons each mounted on a different one of shafts 105, a hydraulic chamber being provided between the pistons and in communication with a confined body of compressible fluid, in the usual manner. The system constituted by the two free-piston engines and the hydraulic spring may thus be considered as analogous to a complete capacitatively coupled oscillating circuit. The reactive energy of the reciprocating masses, plus that of the water in which the unit is submerged, is internally balanced by the hydraulic spring with the result that power efiiciency is considerably increased and, in operation, the apparatus maintains a stable frequency, most of the higher harmonic output being filtered out. When employed in combination with a control system of the type described below, the apparatus constitutes a tuned oscillatory system in which power output is controlled by properly matching the timing of the fuel injectors and valves to the inherent natural frequency of the system.

The apparatus further comprises synchronizing means including two racks 107 each fixed to a different one of the bodies 75 and projecting generally toward the center of the apparatus. As shown, the racks extend parallel to each other with the toothed portions thereof facing each other, and a single pinion 108 is disposed in op erative engagement with both racks. Thus, pinion 108 may have its shaft 109 journaled in a suitable mounting bracket 110, which bracket advantageously also mounts the hydraulic spring 106. It will be understood that the rack and pinion mechanism just described assures ab- 1 1 solutely synchronous operation of the two free-piston engine devices, and that, as the free-piston engine devices function, the rectilinear movement of body 75 results in a corresponding rotational movement of shaft 109.

Control System FIGURE 14 illustrates diagrammatically one form of control system suitable for use in accordance with the invention. For purposes of simplicity of explanation, the control system shown in FIGURE 14 is specially adapted to the apparatus of FIGURE 13. Thus, the control device includes cylinder bodies 75 interconnected by shafts 1115 and energy storing device 106 and also by the synchronizing means comprising racks 107 and pinion 188, described in detail hereinafter with reference to FIGURE 13. Each free-piston engine unit is again provided with two fuel injectors, indicated at 83.

Of conventional construction, fuel injectors 83 each include an actuating member 120, effective to initiate fuel injection, and are operated by linkage 121 to terminate fuel injection, linkage 121 being actuated by servomotor 122. Each piston assembly 79 has secured thereto a slide 123 so disposed as to reciprocate with the piston assembly. Each slide 123 is provided with suitable cam surfaces 124 arranged to operate fuel injector actuators 120. Each slide also comprises a cam surface 125 arranged to operate the actuators for air inlet valves 126, the latter being the valves employed to control the high pressure air during running of the free-piston engines.

Connected to rotary shaft 109 of the synchronizing means is a conventional tachometer 127 constructed to provide an electrical output which has an A.C. component and which is representative of the rotational movement of shaft 109. The output of tachometer 127 is supplied, via a full Wave rectifier 123, to a conventional algebraic adder indicated at 129. Also supplied to algebraic adder 129 is the D.C. voltage output derived from a suitable adjustable voltage source 130 constructed, in any suitable conventional fashion, to provide a D.C. reference voltage of predetermined magnitude. Algebraic adder 129 is operative to compare the rectified output from tachometer 127 with the reference output from device 130 and supplies a corresponding electrical output voltage, via amplifier 131, to operate the servomotor 122.

Accordingly, initiation of fuel injection is accomplished by purely mechanical means phased with the kinematic motion of the engine, such means comprising the appropriate cams 124 and actuators 120, and termination of fuel injection is accomplished, through linkage 121, by actuation of servomotor 122 in accordance with the amplitude of movement of the cylinder body 75 (which constitutes a mass M as represented by the electrical output of tachometer 127.

While actuation of the air valves 126 is accomplished mechanically by cam 125, the actual quantity of :air supplied by these valves of course depends on the pressure of the air delivered to the valves and this pressure is adju-ste automatically by pressure regulators 132 and means which will now be described.

Each slide 123 is provided with a toothed rack portion 133 with which a pinion 134 is operatively meshed, so that pinions 134- rotate in accordance with the reciprocatory movement of the slides 123. Each pinion 134 is connected to drive an electrical tachometer 135, the output of tachometer 135 being supplied, via an amplifier 136, as one input to a conventional phase discriminator 137. The second input to the phase discriminator is derived from tachometer 127, via an amplifier 1313. Phase discriminators 137 are operative to compare the ampl-L fied outputs from tachometers 136 and 127 and, by such comparison, provide a D.C. output proportional to the difference in phase between the two inputs, the latter being supplied in each case to an algebraic adder 139. The second input for each algebraic adder 139 is derived from a device 140 constructed to provide a D.C. reference voltage of a desired predetermined value. Each algebraic adder 139 is constructed to compare (the output of the corresponding phase discriminator 137 with the reference voltage derived from source 1% and provide an electrical output representative of the difference therebetwecn. Such output is supplied, via an amplifier 141 to energize a servomotor 142. Each servomotor 142 is arranged to adjust a different one of the pressure regulators 132.

In considering the operation of the portion of the control system just described, it will be understood that the outputs of the phase discriminator are representative of the efficiency of energy conversion in the free-piston engine devices and that these outputs are employed to correspondingly adjust the magnitude of the air pressure supplied to valves 126. The system controls the energy input by control of initiation and termination of the fuel injection and matches the frequency of the release of energy in the combustion chambers by metering phase differential between the two sets of masses provided by the free-piston engine devices. In this connection, the cylinder body 75 and piston assembly 79 of each freepiston engine device constitute a set of masses (cylinder body mass M and piston assembly mass M and, as hereinbefore described with reference to FIGURE 13, these masses form part of a tuned vibratory system so that the selected tuning of the vibratory system can be taken as a frequency standard.

Starting of the free-piston devices is accomplished by using high pressure air to move the piston assembly of each rapidly through a complete half cycle, after which the diesel operation commences automatically and continues in normal fashion. To accomplish starting in this manner, it is necessary that the piston assembly of each engine be brought to a starting position which may be, for example, at the extreme outward position as FIGURE 14 is viewed. In accordance with this embodiment of the control system, a special starting valve arrangement is provided which operates to (1) admit feed air, that is, air from the output side of the pressure regulators 132, to the cylinders on the side of the pistons facing inwardly, as viewed in FIGURE 14, so that the pistons are accordingly brought to their starting position, and (2) then admit air under full line pressure to the opposite side of the pistons to accomplish the fast starting stroke. For purposes of simplicity, only the portion of the starting valve arrangement associated with the right hand one of the free-piston engines will be described, the starting valve arrangements for both free-piston engines being identical. The starting valve arrangement comprises a feed air control valve 144, provided for control port 1145, and a line air control valve 146 provided for control port 147, the two valves being ganged as indicated at 148. The valves are arranged for actuation by a suitable servomotor 14 energized from a start-stop control device 159. The combination of valves 144 and 146 is so constructed as to have a predetermined operating cycle when actuated by the servo-motor 149, this cycle first opening port 145 to admit feed air to the cylinder and, via port 147 to exhaust, and move the piston to starting position, then closing port 147 to hold on ready to start, then opening both ports 145 and 147 so that the starting stroke occurs because of the pressure of the line air, and then again closing both ports 145 and 147 during running of the engine.

The output of the start-stop control device 15% is also supplied to operate an identical starting control valve associated with the other free-piston engine device.

While the amount of fuel necessary for each power stroke of the free-piston engines remains substantially constant while the engines are running, a greater amount of fuel may be necessary to accomplish starting. Hence, the output of the start-stop control device 1150 may be utilized, in any suitable fashion, to effect a temporary adjustment of reference voltage device in order to ad- 13 just the output thereof in a sense causing increased fuel injection.

The start-stop control device 150', and the reference voltage source 130, may be controlled manually or by any suitable automatic programming means, not shown.

It will be understood from the foregoing that the control system of FIGURE 14 is adapted for use in those embodiments of the invention wherein, as in the embodirneut of FIGURE 13, the tree-piston engine devices constitute part of a tun-ed system. FIGURE 15 illustrates diagrammatically another control means useful in those embodiments wherein, as in FIGURE 3, the system is not tuned. For purposes of simplicity of discussion, the control means of FIGURE 15 will be described with reference to free-piston engine devices constructed in accordance with FIGURE 12.

Thus, the control system of FIGURE 15 is applied to an acoustic energy generating unit comprising two freepiston engine devices 155 constructed in accordance with FIGURE 12 and each including a cylinder body, constituting one mass M and a piston assembly, constituting a second mass M The two free-piston engine devices are mounted in alignment and for free reciprocatory movement in any suitable fashion, such as that illustrated in FIGURE 3 or that illustrated in FIGURE 13. At its outer end, the cylinder body of each device has secured thereto an acoustic piston 156. Centrally of the unit, a rod 157 is fixed to and projects from each cylinder body, the free ends of rods 1157 being pivoted to a rocker arm 158 mounted for oscillation about the axis of shaft 159, as shown. The combination of rods 157, rocker arm 158 and shaft "159 thus constitutes means for synchronizing the reciprocatory movement of the two cylinder bodies, as well as providing a point from which movement representative of such reciprocation can be derived.

At 160, there is indicated a centering spring connected between the two cylinder bodies, such spring being resiliently active in both directions and of any suitable con struction. Thus, the spring at 160 can be a coil spring ofmetal, a pneumatic spring or a hydraulic spring. For consideration of the control system as a whole, it is to be understood that there is an effective total elasticity interposed between the two cylinder bodies and made up by the effect of spring 160, the elastic forces of the various parts of the total assembly such, for instance, as the diaphragms or the like employed to seal around the acoustic pistons 156, and the elastic forces of counterbalance air. The effect of such total elasticity is to localize or fix the center position about which the cylinder bodies work.

Accordingly, the operating frequency of the combined free-piston devices is determined by the frequency induced by the power cycle of the engines and by the action of the bounce chambers of the engines. In this connection, and referring to FIGURE 12, it will be understood that the end portions of cylinder 77 between pistons 82 and walls 78 constitute bounce chambers and that the air pressure therein can be controlled by providing suitable ducting in communication with the bounce chambers and supplying air under pressure thereto via the ducting.

Referring again to FIGURE 15, shaft 159 is connected to drive a device 161 operative to supply an electrical signal representative of the frequency of reciprocatory movement of the cylinder bodies of free-piston engine devices 1 55. Device 161 may take any of various conventional forms. Thus, a standard D.C. tachometer can be employed. There is also provided, as indicated at 162, an electrical voltage source of desired standard or reference frequency. The electrical outputs from devices 161 and 162 are supplied to a conventional device 163 to compare the actual frequency with the standard or reference frequency, device 163 providing a DC. output voltage proportional to the difference in frequency between the outputs of devices 161 and 162. The output voltage from device 163 is supplied, via amplifier 164, to a servomotor 165 operatively arranged 14.- to control a pressure regulating valve 166 in high pressure air supply line 167. The latter is connected in parallel to the bounce chambers of the two free-piston engine devices 155. Hence, the bounce chamber pressure is regulated in accordance with the difference between the actual operating frequency of the free-piston engine devices and the desired frequency.

Connected for actuation by one of the cylinder bodies of the free-piston engine devices is an amplitude pickoff device 163. Device 168 can be of any suitable conventional construction. Thus, for example, the device can comprise a potentiometer the slider of which is connected to the cylinder body of the free-piston engine device in such fashion that the effective value of the potentiometer depends upon the position of the cylinder with which it is associated. Accordingly, the device 168 provides output voltage representative of amplitude of movement of the cylinder bodies and this output voltage is supplied to an alegbraic adder 169 for comparison with the voltage from a reference voltage source 170. Algebraic adder 169 is operative to provide an output voltage representative of the difference between the output of device 168 and the reference voltage supplied by source 171 The output voltage from algebraic adder 169 is supplied, via amplifier 171, to a servomotor 172, the latter being arranged to adjust a fuel control valve 173 in fuel line 174, the fuel line being connected in parallel to the fuel injectors 175 of the two free-piston engine devices 155.

It will thus be understood that the control system of FIGURE 15 is operative to regulate the two valves primarily determinative of the frequency of operation of the free-piston engine devices.

In those cases where the free-piston engine devices employed do not include bounce chambers, the air pressure regulated by servomotor can be the combustion air pressure.

In considering the function of the control system shown in FIGURES 14 and 15, it is to be understood that, with the free-piston devices operating against a constant load, the operating frequency and amplitude are more easily determined by the design parameters of the engines. Thus, without the control systems just described, the freepiston engine devices can be made operative to maintain a frequency of, say, 30 c.p.s. plus or minus 2%. However, when it is necessary to hold frequency very precisely, as in the case of the acoustic energy generating units of the present invention, the 2% limit is excessive and control means such as those just described are required. With the control systems described, the operating frequency is held to very close tolerances, such as plus or minus 0.2% at 30 c.p.s.

What is claimed is:

1. In an underwater signalling system, the combination of submersible means for generating acoustic wave energy in the water, said submersible means comprising a substantially rigid energy generating member disposed for contact with the water and mounted for reciprocatory movement, a reciprocatory combustion engine capable of low frequency operation, and means rigidly interconnecting said generating member and a reciprocatory part of said engine to cause said engine to drive said generating member positively through one half-cycle of reciprocatory movement, and receiving means constructed for actuation by acoustic wave energy in the water and operative to detect the acoustic energy generated by said memher during operation of said engine.

2. An underwater signalling system in accordance with claim 1 and wherein said generating member is fixedly connected to said reciprocatory part of said engine.

3. In a system for detection of underwater bodies at long range by means of acoustic wave energy generating in the water and reflected from the body to be detected, the combination of submersible means for generating such energy, transducer means for receiving the reflected energy and electrical means for deriving a meaningful representation of said reflected energy from the output of said transducer means, said submersible means comprising a substantially rigid energy generating member disposed for contact with the water and mounted for reciprocatory movement, a reciprocatory engine capable of low frequency operation, and means rigidly interconnecting a reciprocatory part of said engine and said generating member to cause said engine to drive said generating member positively through at least one half-cycle of reciprocatory movement, operation of said engine causing low frequency reciprocation of said generating member with a predetermined amplitude of movement and such reciprocation of said member generating in the water acoustic wave energy of substantially sinusoidal form, said transducer means being operable to supply an electrical output including as a component a signal representative of the acoustic wave energy reflected from the body to be detected, and said electrical means including frequency multiplying means and means for recovering said component signal at higher frequency and in substantially pure form.

4. A system in accordance with claim 3 and wherein said engine is a free-piston combustion engine capable of operation at a high power level.

5. In a system for detection of underwater bodies at long range by means of acoustic wave energy generated in the water and reflected from the body to be detected, the combination of submersible free-piston internal combustion engine means for generating such energy, transducer means for receiving the reflected energy and electrical means for deriving a meaningful representation of said reflected energy from the output of said transducer means, said engine means comprising a pair of opposed masses and being operative to move said masses to and from each other at a predetermined relatively low frequency, each of said masses having an acoustic energy generating surface, operation of said engine means causing said surfaces to generate in the water acoustic wave energy of substantially sinusoidal form, said transducer means being operable to supply an electrical output including as a component a signal representative of the acoustic wave energy generated by said surfaces and reflected from the body to be detected, and said electrical means including frequency multiplying means and means for recovering said component signal at higher frequency and in substantially pure form.

6. In an acoustic signaling system for underwater use, the combination of two opposed masses, one of said masses having an outwardly facing energy generating surface, means for supporting said masses with said energy generating surface in contact with the water when said masses are submerged, free-piston internal combustion engine means operatively connected to said masses to move the same to and from each other to cause said surface to generate acoustic wave energy in the water, and control means operatively connected tosaid engine means to cause the same to operate substantially at a predetermined relatively low frequency.

7. In an underwater signalling system, the combination of submersible means for generating acoustic wave energy in the water, said submersible means comprising a substantially rigid acoustic energy generating member disposed to contact the water and mounted for oscillatory movement, a reciprocatory combustion engine capable of low frequency operation, and means interconnecting said acoustic energy generating member and a reciprocatory part of said engine to cause said engine to drive said member positively against the water to generate a train of sonic waves in the low frequency range, and receiving means constructed for actuation by acoustic wave energy in the water and operative to detect the low frequency wave energy generated by said member during operation of said engine.

8. In a submersible apparatus for generating in water acoustic wave energy at a high power level, the combina- 15 tion of a rigid energy generating member mounted for reciprocatory movement and disposed to contact the water, a reciprocatory combustion engine, and means rigidly interconnecting said member and a reciprocatory part of said engine.

9. Apparatus in accordance with claim 8 and wherein said member is fixedly connected to said reciprocatory part.

10. In an apparatus for generating acoustic wave energy in water, the combination of a free-piston engine device, support means carrying said free-piston engine device and by which the same can be supported in a submerged position, said free-piston engine device comprising piston means and cylinder means, one of said means being reciprocatory during operation of said engine device when the same is supported in said submerged position by said support means, a rigid energy generating member, means rigidly interconnecting said generating member and said one reciprocatory means, and means for operating said free-piston engine device in such submerged position.

11. In an apparatus for generating in water acoustic Wave energy of predetermined amplitude and low frequency, the combination of a housing, means for supporting said housing in a submerged position, a free piston engine device comprising a. cylinder body and a piston structure operatively disposed therein, said cylinder body and piston structure each constituting a considerable mass, actuation of said free piston engine device effecting relative reciprocatory movement of said cylinder body and piston structure, means mounting said cylinder body on said housing for free reciprocatory movement relative to said housing, and an energy generating member disposed for contact with the water when said housing is supported in such submerged position, said member being mounted for reciprocatory movement and connected to said cylinder body to be driven thereby.

12. Apparatus in accordance with claim 11 and wherein said member is fixedly attached to said cylinder body.

13. In an apparatus for generating acoustic wave energy in water, the combination of two substantially rigid energy generating members, support means carrying said members and by which said members can be supported in a submerged position, said members being mounted for reciprocatory movement in contact with the water, and engine means disposed between said members and operatively connected thereto to periodically drive said members simultaneously away from each other against the hydrostatic pressure applied to said members by the water.

14. Apparatus in accordance with claim 13, and wherein said engine means is a combustion engine device having two axially aligned reciprocatory parts, said parts being operatively connected each to a different one of said energy generating members.

15. Apparatus in accordance with claim 13, and wherein said engine mean comprises two reciprocatory freepiston engine devices each comprising cylinder means and piston means and disposed with their axes of reciprocation in alignment, said cylinder means being mounted on said support means for reciprocation relative thereto and said energy generating members each being connected to a different one of said cylinder means, said apparatus further comprising synchronizing means interconnecting said cylinder means.

16. Apparatus in accordance with claim 13, and wherein said engine means is a free-piston engine having a pair of opposed pistons, said pistons each being operatively connected to a different one of said energy generating members.

17. In an apparatus for generating acoustic wave energy in water, the combination of two reciprocatory engine devices aligned in the direction of reciprocation, two substantially rigid energy generating members,

means rigidly connecting said members each with a first reciprocatory part of a diiferent one of said engine devices, and synchronizing means interconnecting like reciprocatory parts of said engine devices.

18. In an apparatus for generating acoustic wave energy in water, the combination of two reciprocatory engine devices, support means carrying said devices and by which said devices can be supported in submerged position, said devices being mounted on said support means in alignment in the direction of their reciprocation, two substantially rigid energy generating members, means rigidly connecting said members each with a reciprocatory part of a different one of said engine devices, synchronizing mean interconnecting like reciprocatory parts of said engine devices, and means for operating said engine devices in such submerged position.

19. In an apparatus for generating acoustic wave energy in water, the combination of two reciprocatory engine devices, support means carrying said devices and by which said devices can be supported in submerged position, said devices being mounted on said support means in alignment in the direction of their reciprocation, two substantially rigid energy generating members, means rigidly connecting said members each with a reciprocatory part of a dilferent one of said engine devices, resilient means interconnecting like reciprocatory parts of said engine devices and operative to fix the midpoints about which said like parts reciprocate, and means for operating said engine devices in such submerged position.

20. In an apparatus for generating acoustic Wave energy in water, the combination of a housing adapted to be submerged in the water; two free-piston engine devices each comprising cylinder means and piston means, the cylinder and piston means of each engine device being operatively assembled for relative reciprocation during operation of the engine devices; said engine devices being disposed in said housing; means mounting said engine devices on said housing and comprising means interconnecting said housing and both of said cylinder means for free movement of said cylinder means relative to said housing in the direction of the axes of reciprocation of said engine devices; two acoustic energy generating members each connected to one of said cylinder means and piston means of a diiferent one of said engine devices, said housing having a pair of openings spaced apart in the direction of the axes of reciprocation of said engine devices, and said acoustic energy generating members .each being disposed at a different one of said openings; and means interconnecting said acoustic energy generating members and said housing and closing said openings.

21. In a free-piston engine device, the combination of cylinder means, at least one free-piston disposed in said cylinder means, said engine device comprising means cooperating with said piston to define a combustion chamher, fuel injection means operatively arranged to supply fuel to said injection chamber, and additional means operatively arranged to introduce into said cylinder means a fluid under high pressure to urge said piston in the same direction as the movement resulting from combustion of the injected fuel.

22. In a free-piston engine device, the combination of a cylinder body defining two aligned chambers, a piston assembly including rigidly interconnected pistons each disposed in a difierent one of said chambers, fuel injection means operatively disposed to introduce fuel to one of said chambers, and means for introducing high pressure fluid to the other of said chambers to add to the power resulting from combustion of the injected fuel.

23. In an apparatus for generating acoustic energy in water, the combination of a free-piston engine device comprising a cylinder body defining two aligned chambers, a piston assembly including rigidly interconnected pistons each disposed in a different one of said chambers, fuel injection means operatively arranged to introduce fuel to one of said chambers, means for introducing fluid 18 under pressure to the other of said chambers to add to the power resulting from combustion of the injected fuel, support means carrying said free-piston engine device and by which said device can be supported in submerged position, a rigid acoustic energy generating member connected to one end of said cylinder body and said piston assembly, said cylinder body and piston assembly each constituting a considerable mas-s, and means for supplying said fuel and said fluid to said engine device when the same is supported in submerged position.

24. In a free-piston engine device, the combination of cylinder means defining a first chamber of relatively smaller diameter and a second cylinder of relatively larger diameter, a piston assembly including rigidly interconnected pistons each operatively disposed in a different one of said chambers, fuel injection means operatively arranged to introduce fuel to said first chamber, combustion of the injected fuel generating power to cause relative movement of said cylinder means and piston assembly in one direction, and means for supplying fluid under pressure to said second chamber to add to the power resulting from such combustion.

25. A device in accordance with claim 24 and wherein said last-mentioned means is arranged to supply fluid from an exterior high pressure source directly to said second chamber.

V 26. A device in accordance with claim 24 and wherein said last-mentioned means includes ducting interconnecting said first and second chambers and means arranged to supply fluid from an exterior high pressure source directly to said first chamber.

27. In an apparatus for generating acoustic energy in water, the combination of a submersible support; a freepiston engine device comprising a cylinder body and a piston assembly operatively disposed within said cylinder body; means mounting said cylinder body on said support for reciprocatory movement in the direction of the longitudinal axis of said piston assembly; a rigid acoustic energy generating member; means connecting said energy generating member to one of said cylinder body and said piston assembly, said cylinder body defining two end chambers spaced one on each side of a central chamber of relatively larger diameter, said piston assembly comprising a larger piston operatively disposed in said central chamber and two smaller pistons each rigidly connected to said larger piston and operatively disposed in a different one of said end chambers; fuel injection means operatively arranged to introduce fuel sequentially first to one of said end chambers and then to the other; means for admitting fluid under high pressure to said central chamber sequentially first on one side of said larger piston and then on the other side thereof to add to the power resulting from combustion of the injected fuel, and means for supplying said fuel and said fluid to said engine device when said support is submerged.

28. In an apparatus for generating acoustic energy in water, the combination of a submersible support; a freepiston engine device comprising a cylinder body mounted on said support and defining a central chamber of smaller diameter and end chambers of larger diameter, and two piston assemblies each comprising a smaller piston operatively disposed in said central chamber and a larger piston operatively disposed in one of said end chambers; fuel injection means operatively arranged to introduce fuel to said central chamber between said piston assemblies; means for admitting fluid under pressure simultaneously to said end chambers on the sides of said larger pistons adjacent said central chamber; two rigid acoustic energy generating members each connected to a difierent one of said piston assemblies for actuation thereby, and means for supplying said fuel and said fluid to said engine device when said support is submerged.

29. In an apparatus for generating acoustic energy in water, the combination of a support adapted to be submerged in the water, two free-piston engine devices each including a cylinder body and piston means operatively disposed therein, said cylinder body and piston means of each engine device being arranged for relative reciprocation, means mounting each of said cylinder bodies on said support for free reciprocatory movement in the direction of the relative movement between such cylinder body and its associated piston means, two acoustic energy generating members each connected to a different one of said cylinder bodies for reciprocatory movement therewith, and resilient energy storing means interconnecting said cylinder bodies, said cylinder bodies and resilient energy storing means combining to form part of a tuned vibratory system.

30. In a reciprocatory power apparatus capable of operating at accurately maintained frequency, the combination of a free-piston engine including cylinder means and piston means operatively assembled for relative reciprocatory movement, support means connected to said cylinder means to support said engine and constructed to allow reciprocatory movement of said cylinder means in the direction of the relative movement between said cylinder means and piston means, fuel injection means operatively arranged to supply fuel to the engine, means for admitting to the engine a fluid under pressure to supplement the power supplied by combustion of the injected fuel, means actuated by reciprocatory movement of one of said cylinder means and said piston means and operative to provide a first control output representative of the actual frequency of movement thereof, means providing a second control output representative of the desired frequency of operation of the engine, regulating means operative to adjust the pressure of said fluid supplied to the engine, means for operating said regulating means in accordance with the difference between said first and second control outputs, and means for regulating the amount of fuel supplied by said fuel injection means.

31. Apparatus in accordance with claim 30 wherein said means for regulating the amount of fuel comprises means operative to provide a third control output representative of the amplitude of movement of said cylinder 'body, means operative to provide a fourth control output of predetermined value, and means for adjusting the amount of fuel supplied via said fuel injection means in accordance with the difference between said third and fourth outputs.

32. In a reciprocatory power apparatus capable of operating at accurately maintained frequency, the combination of a free-piston engine including cylinder means and piston means operatively assembled for relative reciprocatory movement, said engine including at least one bounce chamber, support means connected to said cylinder means to support said engine and constructed to allow reciprocatory movement of said cylinder means in the direction of the relative movement between said cylinder means and piston means, fuel injection means peratively arranged to supply fuel to said engine, fluid supply means operatively arranged to supply fluid under pressure to said bounce chamber and including regulating means, means actuated by reciprocatory movement of one of said cylinder means and said piston means and operative to supply a first control output representative of the actual frequency of movement thereof, means providing a second control output representative of the desired operating frequency of said engine, means for operating said regulating means in accordance with the difference between said first and second control outputs, and means for regulating the amount of fuel supplied by said fuel injection means.

33. Apparatus in accordance with claim 32 wherein said means for regulating the amount of fuel comprises means operative to provide a third control output representative of the amplitude of movement of said cylinder body, means operative to provide a fourth control output of predetermined value, and means for adjusting the amount of fuel supplied via said fuel injection means in 20 accordance with the difference between said third and fourth outputs.

34. In a reciprocatory power apparatus capable of operating at accurately maintained frequency, the combination of two free-piston engines each comprising cylinder means and piston means operatively assembled for relative reciprocation, support means connected to said cylinder means to support said engines with said engines disposed with their axes of reciprocation aligned and with said cylinder means both free to reciprocate in the direction of said axes, resilient energy storage means connected between said cylinder means, said cylinder means and energy storage means forming part of a tuned vibratory system, fuel supply means operatively arranged to supply fuel to said engines, pressure fluid supply means operatively arranged to supply fluid to said engines in a manner affecting the operating frequency thereof, means operatively associated with said cylinder means to pro vide a first control output representative of the fundamental frequency of said tuned system, means actuated by at least one of said piston means and operative to provide a second control output representative of the actual operating frequency of said engines, and means operatively associated with said pressure fluid supply means to regulate the same in accordance with the difference between said first and second control outputs.

35. The method for long range underwater signaling comprising submerging in the water an acoustic energy generating member connected to an oscillatory part of a combustion engine capable of high power operation at a substantially constant frequency in the lower portion of the acoustic range; operating said engine to cause reciprocation of said member, in contact with the water, through a definite amplitude and at a definite substantially constant low frequency determined by the operation of said engine, whereby said member generates in the water a train of sonic waves of corresponding frequency; detecting the acoustic energy in the water at a point remote from the location of said energy generating member and at a time when energy generated by said member is present at said point; deriving an electrical signal representative of the total detectable acoustic energy at said point with such signal including a low frequency component representative of energy generated by said member, and isolating said component at higher frequency and in substantially pure form.

36. The method for long range underwater signaling comprising submerging in the water a free-piston reciprocatory engine capable of high power operation at a definite, substantially constant frequency in the lower portion of the acoustic range, operating said engine to generate in the water a train of sonic waves of corresponding frequency, and detecting such sonic waves at a point in the water remote from the location of said engine.

37. In a reciprocatory power apparatus capable of operating at accurately maintained frequency, the combination of an engine including relatively reciprocatory cylinder and piston means, means for supplying an operating fluid to said engine, and control means operative to regulate such supply of fluid, said control means including electrical means responsive to reciprocatory movement of one of said cylinder and piston means and operative to provide a first electrical signal representative of the actual frequency of operation of said engine, other electrical means operative to provide a second electrical signal representative of the frequency at which it is desired to maintain the operation of said engine, means for comparing said signals, and fluid supply regulating means controlled in accordance with the signal comparison effected by said last-mentioned means.

38. In a submersible apparatus for generating in water acoustic wave energy at a high power level, the combination of a housing, a rigid energy generating member mounted for reciprocatory movement relative to said housing, a reciprocatory internal combustion engine 21 mounted in said housing; means rigidly interconnecting said member and a reciprocatory part of said engine, and elongated conduit means extending into said housing and operatively connected to said engine to supply operating fluid thereto and conduct exhaust gases therefrom when the apparatus is submerged.

39. Apparatus in accordance with claim 38 and further comprising means operative to maintain said housing in a given attitude in the water when the apparatus is submerged.

40. Apparatus in accordance with claim 39 and Wherein said last-mentioned means comprises buoyant means connected to said housing.

41. Apparatus in accordance with claim 40 wherein said energy generating member has a flat surface extend ing at right angles to the aXis of reciprocation of said reciprocatory part and said buoyant means is spaced from said housing in a direction parallel to said surface.

42. In a submersible apparatus for generating acoustic wave energy in water, the combination of an energy generating member mounted for reciprocatory movement and disposed to contact the water, drive means connect- 22 ed to said member and by which the same can be reciprocated, and power means connected to said drive means and operative to positively reciprocate said mem ber at a predetermined low frequency to generate in the water acoustic wave energy which is at a high power level and which has said predetermined low frequency.

References Cited in the file of this patent UNITED STATES PATENTS 2,064,911 Hayes Dec. 22, 1936 2,182,063 Striner Dec. 5, 1939 2,424,357 Horsley July 22, 1947 2,840,176 Davis June 24, 1958 2,902,207 Burion Sept. 1, 1959 FOREIGN PATENTS 18,025 Great Britain June 10, 1908 OTHER REFERENCES Submarine Detection by Sonar, by A. C. Keller, Transactions of the American Institute of Electrical Engineers, v01. 66, pp. 1217-1230, 1947. 

